(1) Field of the Invention
The present invention relates to a surface emitting photonic switching structure which, upon receiving signal light of various or varied wavelengths, is capable of selecting a desired wavelength therefrom. The structure is such that the signal light is inputted and outputted in a direction of the thickness of the structure, thereby allowing it to be two-dimensionally integrated and making it to be adapted to photonic switching and optical information processing utilizing wavelength multiplexed signals.
(2) Description of the Related Art
A photonic switching which is equipped with wave-length-division switching function and which has been known is shown in FIG. 1. This has been reported by M. Nishio et al. in Photonic Switching Topical Meeting, Salt Lake City, Utah (March, 1991) pp. 246-249 under the title "High-speed Wavelength Switching Experiment for Wavelength-Division and Time-Division Hybrid Switching Networks using LiNbO.sub.3 Fabry-Perot Tunable Wavelength Filters". This structure uses X-cut LiNbO.sub.3 substrate 10 and the waveguide length (cavity length) is set at 1 mm. Both the facets are coated with anti-reflection coatings 11 and 12. Anti-reflection coated cleaved-ended single fibers 13 and 14 are coupled with an optical waveguide 15. The transmission wavelength tuning is accomplished by changing the refractive index of the Fabry-Perot resonator with control voltages Vc applied across electrodes. FIG. 2 shows the measured wavelength and transmission ratio. In this example, the voltage of 50V applied results in a resonance wavelength shift of 3 Angstroms. The exemplified structure is one in which the light enters laterally, and no examples have been reported which relate to a surface emitting type and which enable the two-dimensional integration.
The problems in the conventional examples described above reside not only in the impossibility of two-dimensional integration but also in the necessity of increasing the element length and of applying such a high operating voltage as 50V. The element length becomes long because the element is cut out from the bulk LiNbO.sub.3 and thus the need of the length being about 1 mm is inevitable. Also, for tuning the refractive index of the Fabry-Perot resonator, use is made of the electrical-optical characteristics of LiNbO.sub.3, and this mechanism unavoidably leads to the need of using a high operating voltage as described above.